The present invention relates to the use of aldehyde donors, such as 1,3-bis(hydroxymethyl)-5,5-dimethylhydantoin, to stabilize peroxides in aqueous solutions and in particular circulating water slurries in papermaking applications.
The bleaching of wood fibers frequently involves the use of peroxides, such as hydrogen peroxide. Hydrogen peroxide, however, is readily decomposed by catalase, an enzyme often found in recycled water (i.e. water from processing recycled paper). Most aerobic bacteria synthesize peroxide-degrading enzymes (e.g. catalase and peroxidase) as a defense against free-radical-producing peroxides that are formed during cell respiration. In a mill white water environment, temperatures and the availability of nutrients encourage bacterial growth. The presence of hydrogen peroxide stimulates bacteria to generate catalase to destroy it, sometimes enough to hamper or disable a hydrogen peroxide treatment stage. As a result, peroxide stability is limited and bleaching effectiveness is reduced. The conditions of recycled paper processing, deinking and bleaching are especially conducive to enzyme peroxide degradation.
Some of the methods employed to stabilize hydrogen peroxide include biocide treatments (e.g. peracetic acid treatment), use of high hydrogen peroxide dosages and steep bleaching.
U.S. Pat. No. 5,728,263 describes the use of dialdehydes and acetals thereof, such as glutaraldehyde, to inhibit the decomposition of peroxide in the treatment of recycled and other fiber pulps. Hydrogen peroxide stability is enhanced by the addition of glutaraldehyde. Glutaraldehyde, however, has a poor safety profile and high concentrations of it are required to inhibit peroxide decomposition.
U.S. Pat. No. 5,885,412 describes the use of certain hydroxyl amines and alkyl derivatives, including hydroxylammonium sulfate, ascorbic acid and formic acid, that suppress or inhibit hydrogen peroxide degradation by enzymes, such as peroxidases and catalases, during bleaching of cellulose fibers and do not affect microorganisms.
Great Britian Patent Publication No. 2,269,191 describes the use of an organic peracid that has a disinfectant effect on catalase producing microorganisms at neutral or acidic pH.
U.S. Pat. No. 4,908,456 teaches the use of methylolated hydantoin, especially 1,3-dimethylol-5,5-dimethylhydantoin (DMDMH) as an antimicrobial agent.
U.S. Pat. No. 5,405,862 teaches the preparation of low free formaldehyde DMDMH compositions which are used in biocidal effective amounts in any medium in which microbial growth is to be retarded.
There is a need for a method of stabilizing hydrogen peroxide in the presence of catalase and other peroxide degenerating enzymes that is not hazardous.
The present invention is a method of stabilizing hydrogen peroxide in an aqueous solution, such as a circulating water slurry, comprising a peroxide, such as hydrogen peroxide. The aqueous solution may include organic matter. The method comprises adding an aldehyde donor, such as a methylolhydantoin, to the solution (or slurry). The inventors have discovered that aldehyde donors significantly reduce the decomposition of hydrogen peroxide by catalase and other peroxide decomposing enzymes, which are often present in recycled paper. As a result, less hydrogen peroxide needs to be added to a solution to effectively bleach organic matter in the solution. Furthermore, aldehyde donors are safe to handle and cost effective.
Another embodiment is a method of bleaching recycled papers in a circulating water slurry comprising organic matter. The method comprises adding hydrogen peroxide and an aldehyde donor to the slurry.
Yet another embodiment is a method of inhibiting catalase and/or other peroxide decomposing enzymes in an aqueous solution, such as a circulating water slurry, comprising adding an aldehyde donor to the aqueous solution.
Yet another embodiment is a method of stabilizing a peroxide in an aqueous solution comprising maintaining a peroxide stabilizing effective amount of at least one aldehyde donor in the aqueous solution.
Yet another embodiment is a method of inhibiting catalase and/or other peroxide decomposing enzymes in an aqueous solution, such as a circulating water slurry, comprising maintaining a peroxide decomposing enzyme inhibiting effective amount of at least one aldehyde donor in the aqueous solution.
In any identified embodiments, the term xe2x80x9caboutxe2x80x9d means within 50%, preferably within 25%, and more preferably within 10% of a given value or range. Alternatively, the term xe2x80x9caboutxe2x80x9d means within an acceptable standard error of the mean, when considered by one of ordinary skill in the art.
The present invention provides a method of stabilizing a peroxide, such as hydrogen peroxide, in an aqueous solution comprising the peroxide. The method comprises adding to or maintaining an aldehyde donor in the aqueous solution. Generally, the peroxide is added to the solution in the form of a bleaching solution.
The aqueous solution can be (i) a circulating water slurry comprising organic matter or (ii) a slurry dilution water. Generally, a slurry dilution water contains little ( less than 0.2% by weight), if any, organic matter. Slurry dilution waters are frequently added to dilute or form solutions containing organic matter, especially pulp. Furthermore, slurry dilution water is frequently recovered from circulating water slurries containing organic matter by methods known in the art.
The term xe2x80x9caldehyde donorxe2x80x9d as used herein is defined as any material which is not an aldehyde but upon aqueous dilution liberates a compound which gives positive reactions with aldehyde identifying reagents, i.e. a compound which can identify aldehyde groups. Generally, the liberated compound has the formula 
where R is any functional group. In other words, the term xe2x80x9caldehyde donorxe2x80x9d includes any compound which is not an aldehyde but when hydrolyzed forms an aldehyde or a compound which gives positive reactions with aldehyde identifying reagents. Examples of aldehyde identifying reagents include, but are not limited to, Benedicts solution, Tollens reagent, and acetyl acetone.
Suitable aldehyde donors include, but are not limited to, imidazolidinyl urea, Quatemium-15, diazolidinyl urea, bromonitropropanediol, methenamine, 5-bromo-5-nitro-1,3-dioxane, sodium hydroxymethylglycinate, 3,5-dimethyl-1,3,5,2H-tetrahydrothiadiazine-2-thione, hexahydro-1,3,5-tris(2-hydroxyethyl)triazine, hexahydo-1,3,5-triethyl-s-triazine, polymethoxy bicyclic oxazolidine, tetrakis (hydroxymethyl) phosphonium sulfate, methylolhydantoins, and any combination of any of the foregoing.
Preferred aldehyde donors include, but are not limited to, methylolhydantoins, such as monomethyloldimethylhydantoins (MMDMHs), dimethyloldimethylhydantoins (DMDMHs), and any combination of any of the foregoing. Examples of methylolhydantoins include, but are not limited to, 1-hydroxymethyl-5,5-dimethylhydantoin (a MMDMH), 3-hydroxymethyl-5,5-dimethylhydantoin (a MMDMH), and 1,3-bis(hydroxymethyl)-5,5-dimethylhydantoin (DMDMH) mixtures (which are available as aqueous solutions under the tradenames Dantogard(copyright) and Glydant(copyright) from Lonza Inc. of Fair Lawn, N.J.). Other preferred aldehyde donors include, but are not limited to, low free formaldehyde compositions of dimethyloldimethylhydantoin, such as those described in U.S. Pat. No. 5,405,862, which is hereby incorporated by reference. Preferably, the aldehyde donor has a free formaldehyde concentration of less than 0.2% based on 100% total weight of aldehyde donor. Low free formaldehyde compositions reduce workplace exposure risk to formaldehyde. Generally, the weight ratio of methylolhydantoins to peroxide ranges from about 10:1 to about 1:1000.
According to a preferred embodiment, the aldehyde donor is a mixture of 1-hydroxymethyl-5,5-dimethylhydantoin, 3-hydroxymethyl-5,5-dimethylhydantoin, and 1,3-bis(hydroxymethyl)-5,5-dimethylhydantoin. Preferably, the mixture has a free formaldehyde concentration of less than 0.2% by weight, based on 100% total weight of the mixture. An example of a preferred mixture is a 65-70% aqueous solution of MMDMH, DMDMH, and 5,5-dimethylhydantoin (DMH) available under the tradename Dantogard(copyright) 2000 from Lonza, Inc of Fair Lawn, N.J.
The aldehyde donor significantly reduces the decomposition rate of hydrogen peroxide by catalase and other peroxide decomposing enzymes. The amount of the aldehyde donor added to the solution is typically sufficient to maintain a peroxide stabilizing effective concentration (i.e. a concentration sufficient to prevent decomposition of the peroxide) and/or a peroxide decomposing enzyme inhibiting effective concentration in the solution (such as a catalase inhibiting concentration). According to a preferred embodiment, the concentration of aldehyde donor maintained in the slurry is less than a microbicidally effective amount. Preferably, the concentration of aldehyde donor maintained in the solution ranges from about 1 to about 1,000 ppm, more preferably from about 30 to about 200 ppm, and most preferably from about 60 to about 120 ppm. According to one embodiment, the concentration of aldehyde donor maintained in the solution ranges from about 1 to about 5000 ppm, from about 100 to about 1000 ppm, from about 250 to about 500 ppm, from about 250 to about 750 ppm, from about 50 to about 500 ppm, from about 50 to about 750 ppm, from about 100 to about 200 ppm, or from about 200 to about 400 ppm.
Although many of the aldehyde donors identified above are also known biocides, their concentration in the solution can be less than that necessary to have a significant biocidal effect, i.e. they generally provide less than a 2 log reduction in the microorganism population in short contact time applications (e.g. 3 hours or less). The term xe2x80x9clog reduction in the microorganism populationxe2x80x9d refers to the difference between the logarithm (base 10) of the microorganism count of an untreated substrate after a given contact time, such as 3 hours or less, and the logarithm of the microorganism count of an identical substrate treated with an aldehyde donor after the same contact time. According to one embodiment, the aldehyde donor causes a log reduction in microorganism population of less than 0.5 or 1.
A biocidal concentration of one or more biocides may also be added to or maintained in the solution. Suitable biocides include, but are not limited to, those described in Great Britain Patent Publication No. 2,269,191 ,which is hereby incorporated by reference. Other suitable biocides include, but are not limited to, thiocarbamates, such as sodium dimethyl dithiocarbamate; glutaraldehyde; dibromo nitrile propionamide (DBNPA); bromnitropropanediol; tetrakis (hydroxymethyl) phosphonium sulfate; bromonitrostyrene (BNS); benzisothiazolones; methylene bis(thiocyanate); 2-mercaptobenzothiazole (MBT); isothiazolines, including 5-chloro-2-methyl-4-isothiazolin-3 -one (CMI), 2-methyl-4-isothiazolin-3 -one (MI), octyl-4-isothiazolin-3-one, and mixtures thereof; bistrichloromethylsulfone (BTCMS); quaterary ammonium compounds, such as alkyldimethylbenzyl ammonium chlorides and dialkydimethyl ammonium chlorides; 2-bromo-4-hydroxyacetophenone (BHAP); and 5-oxo-3,4-dichloro-1,2-dithiol; and any combination of any of the foregoing.
Peracetic acid may be added to the solution to kill or inhibit the growth of microorganisms and/or to bleach any organic matter in the solution. Therefore, a microbicidally effective amount and/or a bleaching effective amount of peracetic acid may be added to or maintained in the solution.
The aldehyde donor may be added directly to the solution (e.g. slurry or slurry dilution water) or bleaching solution as a solid or liquid. Preferably, the aldehyde donor is added to the solution as a liquid. For example, the aldehyde donor may be added as an aqueous mixture. The concentration of aldehyde donor in such an aqueous mixture typically ranges from about 5 to about 95% by weight and preferably from about 20 to about 75% by weight, based upon 100% weight of total mixture. The aldehyde donor may be added before, simultaneously with, or after the hydrogen peroxide is added to the aqueous solution, or alternatively to the peroxide bleaching solution itself.
The hydrogen peroxide may be added alone or as a mixture with one or more biocides to the solution (or slurry) or peroxide bleaching solution. For example, a mixture of hydrogen peroxide and peracetic acid may be added to the solution (or slurry) or peroxide bleaching solution.
According to one embodiment, a blend of one or more aldehyde donors, CMI, and MI is added to the solution (or slurry). The blend may optionally contain isothiazoline stabilizers as known in the art. A preferred blend includes CMI, MI, and at least one of MMDMH and DMDMH. According to another embodiment, a blend of one or more aldehyde donors and a benzisothiazolinone is added to the solution (or slurry). A preferred blend includes benzisothiazolinone and at least one of MMDMH and DMDMH. Such aldehyde donor blends are described in U.S. Pat. Nos. 6,121,302 and 6,114,366, which are incorporated herein by reference.
The concentration of hydrogen peroxide added to or maintained in the solution is typically a bleaching effective concentration in the solution. The concentration of hydrogen peroxide maintained in the solution preferably ranges from about 1 to about 50,000 ppm, more preferably ranges from about 10 to about 10,000 ppm, and most preferably ranges from about 100 to about 1,000 ppm.
The solution may be, for example, a pulp slurry, a papermaking slurry, a mineral slurry or white water. White water is generally separated liquid that is re-circulated to a preceding stage of a papermaking process, especially to the first disintegration stage, where paper, water and chemicals are mixed.
Generally, a mineral slurry comprises of from about 50 to about 80% by weight of mineral matter, such as, but not limited to, calcium carbonate or clay. The mineral slurry may also contain an organic dispersing agent. Preferred organic dispersing agents include, but are not limited to, polyacrylates.
Typical pulp slurries in paper applications contain from about 0.2 to about 18% by weight of organic matter, based upon 100% total weight of slurry. The organic matter is typically comprised of wood fiber (or pulp) and adjuvants, such as sizing and starch. Generally, the organic matter comprises from about 90 to about 99% by weight of wood fiber (or pulp), based upon 100% total weight of organic matter. According to a preferred embodiment, the wood fiber is at least partially derived from recycled paper.
The pulp slurry may also contain other adjuvants known in the art. Examples of such adjuvants include, but are not limited to, slimicides; sodium hydroxide (or other caustic); peroxide stabilizers, such as sodium silicate, magnesium sulfate, and polyphosphates; chelating agents, such as EDTA; fatty acids; and combinations thereof.
Generally, the pH of the solution ranges from about 7 to about 13 and preferably from about 8 to about 11. In another embodiment, the pH of the solution ranges from about 4 to about 13, preferably from about 7 to about 12, and more preferably from about 8 to about 11.
The following examples are intended to describe the present invention without limitation.